1. Field of the Invention
The present invention relates to a method for dyeing acid-modified polyester fibers with a cationic dye bath containing a specific thiazoleazo cationic dye.
2. Description of the Prior Art
Of the various synthetic fibers available, the demand for polyester fibers increases every year due to the superior properties of polyester as a fiber. Polyester fiber is rendered dyeable with a cationic dye by modifying the fiber with acidic substances, as disclosed in, for example, Japanese Patent Publication No. 10497/59. Acid-modified polyester fibers, as disclosed hereinbefore and in U.S. Pat. No. 3,018,272 are well-known. For cationic dyes for acid-modified polyester fibers, it is, of course, possible to dye the fibers a brilliant shade which is a characteristic of a cationic dye. Moreover, cationic dyes for acid-modified polyester fibers must also have the following properties superior to the properties of conventional cationic dyes:
I. higher fastness to light on the acid-modified polyester fiber, PA1 Ii. less decomposition during high temperature dyeing, PA1 Iii. good compatibility with other dyes of different shade (the same dyeing rate), and PA1 Iv. less staining of or less decomposition due to other fibers, such as wool or regular polyester fibers, frequently used in blends with acid-modified polyester fibers.
As disclosed in German Offenlegungsschrift No. 2,129,271 and Belgian Pat. No. 728,033, it is well-known that thiazoleazo-type cationic dyes can be applied to acid-modified polyester fibers. On the other hand, it is also well-known that dyes having a structure similar to the present dyes can be advantageously applied to acrylic fibers, as disclosed in Japanese patent publication No. 15791/71, Netherlands specification No. 6,608,698 and British Pat. No. 787,369 in addition to the above German and Belgian patents. However, these dyes which are useful for dyeing acrylic fibers are not necessarily useful for dyeing acid-modified polyester fibers because the dyes, particularly the blue dyes thereof, provide dyeings having a lower fastness to light on an acid-modified polyester fiber than on an acrylic fiber, and, moreover, the dyes should be applied to the fiber using high temperature dyeing (about 110.degree. to 130.degree.C) or carrier dyeing under more severe conditions than the conditions of 90.degree. to 100.degree.C used with an acrylic fiber.
Therefore, the dyes must have higher fastness to light and higher stability to high temperatures than is required for acrylic fibers, i.e., in order for the dyes to be applied to acid-modified polyester fibers.
An acid-modified polyester fiber is more frequently used in blends with other fibers, such as wool, other types of polyesters, polyamides or celluloses, than is an acrylic fiber, and the effects of these fibers used in the blends on the cationic dyes during dyeing cannot be ignored. For example, the dyes are sometimes decomposed by a reductive group present in the blend of fibers.
The dyeing of acid-modified polyester fibers using thiazoleazo-type blue dyes has been studied, and it has been found that blue dyes are exhausted so much faster than the other cationic dyes of different shades that level dyeings do not result and these dyes are not suitable for combination dyeing. In addition, it was found that the same phenomenon was also observed when these dyes were applied to acrylic fibers in trichromatic dyeing as one of the three primary colors compatible with each other.
In addition, it was found that dyeings of lower fastness to light on an acid-modified polyester fiber resulted than on an acrylic fiber. These factors are, of course, due entirely to the differences between acrylic fibers and acid-modified polyester fibers.
It is clear from the above that conventionally employed thiazoleazo-type blue dyes cannot be used satisfactorily as a dye for acid-modified polyester fibers.